Gas oil composition

ABSTRACT

To provide a gas oil composition providing superior low temperature performance as compared with the conventional techniques. 
     The gas oil composition, wherein a sulfur content is 1 ppm by mass or less, an aromatic content is 1% by mass or less, a C5-C15 paraffin content is 30% to 85% by mass, a C20-C27 paraffin content is 3% to 20% by mass, and a isoparaffin content is 50% to 75% by mass, contains a cold flow improver at 20 ppm to 1000 ppm by mass.

TECHNICAL FIELD

The present invention relates to a gas oil composition, in particular toa gas oil composition which can be used in a very low temperatureenvironments.

BACKGROUND ART

In general, a gas oil composition is produced by blending one or moretypes of blendstocks produced by subjecting a straight gas oil orstraight kerosene, produced through an atmospheric distillation unit ofcrude oil to hydrorefining or hydrodesulfurization. In particular, it isoften the case that the blend ratio of the foregoing kerosene blendstockand gas oil blendstock is controlled in order to ensure low temperaturefluidity during a winter season. If necessary, the blendstocks areblended with additives such as cetane number improvers, detergents, andcold flow improvers.

In recent years, the use of Fischer Tropsch synthetic oil (hereinafter,referred to as “FT synthetic oil”) obtained by Fischer Tropsch synthesisusing carbon monoxide and hydrogen as feedstocks, as one of alternativefuels for a petroleum-based fuel is considered. When gas oil for dieselfuel is produced from FT synthetic oil, gas oil free of sulfur contentcan be obtained. Thus, the FT synthetic gas oil is preferable in termsof reducing environmental impact.

However, the above-described FT synthetic oil has a relatively highcontent of straight-chain saturated hydrocarbon (normal paraffin)compounds. It has been pointed out that in particular when heavy normalparaffin compounds are contained, there is the possibility that theywould deposit in the form of wax. Further, the FT synthetic blendstockis a hydrocarbon mixture containing predominantly the aforesaid normalparaffin and saturated hydrocarbons having a side chain (isoparaffin)and thus generally has poor oil solubility. Accordingly, there is a casethat additives to be dissolved in fuel oils such as gas oil, highlyrelying on their oil soluble groups (straight-chain alkyl group or thelike) would be hardly dissolved. With this being the situation, therehas been a problem in that gas oil derived from FT synthetic oil cannotbe used in a low temperature environment.

In order to solve the above problem, various techniques have beendeveloped. For example, JP 2007-270109 A (PTL 1) discloses a techniqueof adding and mixing a lubrication improver and a cold flow improver toand with a FT synthetic gas oil composition having a certain compositionto thereby improve the fluidity in a low temperature environment.

CITATION LIST Patent Literature

PTL 1: JP 2007-270109 A

SUMMARY OF INVENTION Technical Problem

However, considering the use of a gas oil composition in cold climateareas such as the Arctic Circle or the Antarctic Circle, the FTsynthetic gas oil composition obtained by the technique described in PTL1 would not exhibit sufficient fluidity. Therefore, it has been requiredto improve the low temperature performance.

Further, when the aforesaid FT synthetic gas oil is used as fuel for adiesel engine, in order to keep favorable startability in enginecombustion and stability in idling, the kinetic viscosity at 30° C. isrequired to be high. On the other hand, in order to improve the fluidityin a low temperature environment, the pour point is required to be low.In short, since there is a trade-off between the favorable kineticviscosity and the favorable pour point, it has been difficult to achievethe both using conventional techniques. Therefore, it is desirable todevelop a technique making it possible to improve the fluidity withoutreducing the kinetic viscosity even in a severe low temperatureenvironment.

The present invention was made in view of the above circumstances, andan object thereof is to provide a gas oil composition that providessuperior low temperature performance as compared with the conventionaltechniques even if it contains as a feedstock, an oil having a highnormal paraffin content, such as an FT synthetic oil.

Solution to Problem

The inventors of the present invention made various studies on the aboveproblem to find that excellent fluidity in a low temperature environmentcan be realized without reducing the kinetic viscosity, by optimizingthe composition of a gas oil composition and also adding a certainamount of a cold flow improver to the gas oil composition.

The invention is made based on such findings, and the summary is asfollows.

-   (1) A gas oil composition, wherein a sulfur content is 1 ppm by mass    or less, an aromatic content is 1% by mass or less, a C5-C15    paraffin content is 30% to 85% by mass, a C20-C27 paraffin content    is 3% to 20% by mass, and a isoparaffin content is 50 to 75% by    mass,

characterized in that the gas oil composition comprise a cold flowimprover at 20 ppm to 1000 ppm by mass.

-   (2) The gas oil composition according to (1), wherein the pour point    is −70° C. to −35° C. and the kinetic viscosity at 30° C. is 1.5    mm²/s to 4.0 mm²/s.-   (3) The gas oil composition according to (1), comprising Fischer    Tropsch synthetic oil.

Advantageous Effect of Invention

The present invention makes it possible to provide a gas oil compositionproviding superior low temperature performance as compared with the caseof using the conventional techniques even if an oil having a high normalparaffin content is used as a feedstock.

DESCRIPTION OF EMBODIMENTS

The invention of the present application is described below in detail.

A gas oil composition of the present invention has a sulfur content of 1ppm by mass or less, an aromatic content of 1% by mass or less, a C5-C15paraffin content of 30% to 85% by mass, a C20-C27 paraffin content of 3%to 20% by mass, and an isoparaffin content of 50% to 75 by mass; andcontains 20 ppm to 1000 ppm by mass of a cold flow improver.

(Sulfur Content, Aromatic Content)

The gas oil composition of the present invention has a sulfur content of1 ppm by mass or less and an aromatic content of 1 by mass or less. Inorder to further reduce particulates emitted from a diesel engine, andin terms of further improving the fuel efficiency, the sulfur content is1 ppm by mass or less and the aromatic content is 1% by mass or less.

(C5-C15 Paraffin Content)

The gas oil composition of the present invention has a C5-C15 paraffincontent of 30% to 85% by mass, preferably 40% to 70% by mass. The C5-C15paraffin content is limited to 30% by mass or more in terms of improvingthe startability of a diesel engine and the stability in idling, and islimited to 85% by mass or less in terms of reducing the particulatesemitted from the diesel engine.

(C20-C27 Paraffin Content)

The gas oil composition of the present invention has a C20-C27 paraffincontent of 3% to 20% by mass, preferably 7% to 16% by mass. The C20-C27paraffin content needs to be 3% by mass or more for favorable solubilityof the cold flow improver, and needs to be 20% by mass or less forfavorable low temperature fluidity of the gas oil composition.

(Isoparaffin Content)

The gas oil composition of the present invention has an isoparaffincontent of 50% to 75% by mass, preferably 60% to 70% by mass. In orderto improve the startability and operability at a low temperature, theisoparaffin content needs to be 50% by mass or more, whereas in order toobtain a gas oil composition with high yield, the isoparaffin contentneeds to be 75% by mass or less.

(Mass Ratio Between Normal Paraffin and Isoparaffin)

Further, the mass ratio of the normal paraffin content with respect tothe isoparaffin content (normal paraffin content/isoparaffin content) ispreferably in the range of 0.3 to 1.0, more preferably in the range of0.4 to 0.7. In terms of improving the startability in the combustion andthe stability in idling of a diesel engine under very low temperatureweather conditions, the mass ratio (normal paraffin content/isoparaffincontent) is preferably 0.3 or more. Since a certain amount ofisoparaffin is contained due to isomerization in order to achievefavorable startability and operability at low temperatures, the massratio is preferably 1.0 or less.

(Distillation Properties)

The gas oil composition of the present invention preferably has a 5%distillation temperature of 140° C. to 200° C., more preferably 150° C.to 195° C. In order to improve the startability of a diesel engine andthe stability in idling, the 5% distillation temperature is 140° C. ormore, whereas in order to achieve favorable startability and operabilityat low temperatures, the 5% distillation temperature is preferably 200°C. or less.

Further, the gas oil composition of the present invention preferably hasa 95% distillation temperature of 300° C. to 340° C., more preferably310° C. to 330° C. In terms of improving, the specific fuel consumptionof a diesel engine, the 95% distillation temperature is preferably 300°C. or more, whereas in terms of reducing particulates emitted from thediesel engine, the 95% distillation temperature is preferably 340° C. orless.

(Density)

The gas oil composition of the present invention preferably has adensity at 15° C. of 0.750 g/cm³ to 0.780 g/cm³, more preferably 0.760g/cm³ to 0.780 g/cm³. The density at 15° C. is 0.750 g/cm³ or more forfavorable specific fuel consumption of a diesel engine, and is 0.780g/cm³ or less for favorable low temperature fluidity of the gas oilcomposition.

(Cloud Point)

Further, the gas oil composition of the present invention preferably hasa cloud point of −35° C. or less, more preferably −55° C. or less so asto withstand the use under very low temperature weather conditions. Thecloud point used herein means the pour point measured based on JIS K2269 “Testing method for pour point and cloud point of crude oil andpetroleum products”.

(Kinetic Viscosity at 30° C.)

The gas oil composition of the present invention preferably has akinetic viscosity at 30° C. of 1.5 mm²/s to 4.0 mm²/s, more preferably2.0 mm²/s to 3.5 mm²/s. The kinetic viscosity at 30° C. is 1.5 mm²/s ormore in terms of improving the startability of a diesel engine or thestability in idling, and is preferably 4.0 mm²/s or less in terms ofreducing particulates emitted from the diesel engine.

(Pour Point)

The pour point of the gas oil composition of the present invention ispreferably −35° C. or less. In order to achieve favorable lowtemperature fluidity under very low temperature weather conditions, thepour point is preferably −35° C. or less, more preferably −55° C. orless.

The pour point need not be lower than necessary, and the pour point ispreferably −70° C. or more, more preferably −66° C. or more in terms ofthe production cost of the gas oil composition.

(Cold Flow Improver)

The gas oil composition of the present invention is required to contain150 ppm to 1000 ppm by mass of a cold flow improver, the content of thecold flow improver is preferably 150 ppm to 500 ppm by mass, morepreferably 200 ppm to 300 ppm by mass. The content (addition amount) ofthe cold flow improver is 150 ppm by mass or more in order to prevent afilter of a diesel powered automobile from being plugged in a lowtemperature situation, and is 1000 ppm by mass or less in terms of theeffectiveness of the cold flow improver and the economic efficiency.

As the cold flow improver, ethylene-vinyl acetate copolymer and/or coldflow improver having a surfactant effect are/is used. Examples of thecold flow improver having a surfactant effect include one or moreselected from copolymers of ethylene and methyl methacrylate, copolymersof ethylene and α-olefin, chlorinated methylene-vinyl acetatecopolymers, alkyl ester copolymers of unsaturated carboxylic acids,esters synthesized from nitrogen-containing compounds having a hydroxylgroup and saturated fatty acids and salts of the esters, esters andamide derivatives synthesized from polyhydric alcohols and saturatedfatty acids, esters synthesized from polyoxyalkylene glycol andsaturated fatty acid, esters synthesized from alkyleneoxide adducts ofpolyhydric alcohols or partial esters thereof and saturated fatty acids,chlorinated paraffin/naphthalene condensates, alkenyl succinamides, andamine salts of sulfobenzoic acids.

(Lubricity Improver)

The gas oil composition of the present invention preferably contains alubricity improver at a concentration of 20 mg/L to 300 mg/L, morepreferably 50 mg/L to 200 mg/L. With the addition amount of thelubricity improver being within the range of 20 mg/L to 300 mg/L, theefficacy of the added lubricity improver can be effectively exerted. Forexample, for a diesel engine equipped with a distributor injection pump,increase in the driving torque of the pump in operation can besuppressed and the wear of the pump can be reduced.

As for the type of the lubricity improver, a lubricity improvercontaining a compound which comprises a fatty acid and/or a fatty acidester and has a polar group is used. There is no particular restrictionon the specific name of the compounds and so on. For example, any one ormore selected from carboxylic acid-, ester-, alcohol- and phenol-basedlubricity improvers can be used. Out of those, carboxylic acid- andester-based lubricity improvers are preferred. Examples of thecarboxylic acid-based lubricity improver include linoleic acid, oleicacid, salicylic acid, palmitic acid, myristic acid or hexadecenoic acidor a mixture of two or more of these carboxylic acids. Carboxylic acidesters of glycerin can be given as an example of the ester-basedlubricity improver. The carboxylic acid ester may include one or morecarboxylic acids. Specific examples of the carboxylic acids includelinoleic acid, oleic acid, salicylic acid, palmitic acid, myristic acid,and hexadecenoic acid. The weight-average molecular weight of the activecomponent of the lubricity improver is preferably 200 or more and 1000or less in order to enhance the solubility to the gas oil composition.

(Other Additives)

In order to further enhance the properties of the gas oil compositionsof the present invention, other known fuel oil additives mentioned later(hereinafter referred to as “other additives” for convenience) may beused alone or in combination. Examples of the other additives includephenolic- and aminic-antioxidants; metal deactivators such assalicyliden derivatives; anti-corrosion agents such as aliphatic aminesand alkenyl succinic acid esters; anti-static additives such as anionic,cationic, and amphoteric surfactants; coloring agents such as azo dye;silicone-based antifoaming agents and antifreezing agents such as2-methoxyethanol, isopropyl alcohol, and polyglycol ethers.

The amounts of the other additives may be set to any value. Especially,the amount of each of the other additives is preferably 0.5% by mass orless, more preferably 0.2% by mass or less, on the basis of the totalamount of the gas oil composition.

There is no particular restriction on the other specifications of adiesel engine in which the gas oil composition of the present inventionis used, the applications thereof, and the environment where the gas oilcomposition is used.

(FT Synthetic Oil)

The gas oil composition of the present invention preferably furthercontains Fischer Tropsch synthetic oil (FT synthetic oil). As describedabove, the FT synthetic oil contains a relatively large amount ofstraight-chain saturated hydrocarbon (normal paraffin) compounds andaccordingly, a gas oil derived from an FT synthetic oil cannot be usedin a low temperature environment, which has been a problem. Thus, theadvantageous effect of the present invention can be exerted mostsignificantly.

Further, in order to suppress the consumption of oil base blendstock byusing an FT synthetic oil in terms of alternative fuels for petroleum,the gas oil composition preferably contains an FT synthetic oil.

For example, the FT synthetic oil can be obtained by a production methodincluding the steps of fractionating an FT synthesis oil into a lightfraction and a wax fraction, hydroisomerizing the light fraction toobtain a hydroisomerized oil, hydrocracking the wax fraction to obtain ahydrocracked oil, mixing the hydroisomerized oil and the hydrocrackedoil and then supplying it to a product fractionator, and adjusting thecutting temperature at the product fractionator so as to obtain akerosene composition of the invention. Moreover, it is preferable torecycle a bottom oil of the product fractionator and mix it with the waxfraction and then hydrocrack it thereby obtaining the hydrocracked oil.

Furthermore, the light gas oil blendstock and a heavy gas oil blendstockobtained from the product fractionator may be mixed at a predeterminedratio, thereby producing a gas oil composition of the present invention.The light gas oil blendstock and the heavy gas oil blendstock have asulfur content of 1 ppm by mass or less and an aromatic content of 1% bymass or less. The light gas oil blendstock preferably has a density of0.740 to 0.760, a 5% distillation temperature of 155° C. to 175° C.; a95% distillation temperature of 230° C. to 250° C., a C5-C15 paraffincontent of 90% to 99.9% by mass, and an isoparaffin content of 40% to55% by mass. The heavy gas oil blendstock preferably has a density of0.770 to 0.790, a 5% distillation temperature of 240° C. to 260° C., a95% distillation temperature of 330° C. to 350° C., a C5-C15 paraffincontent of 15% to 35% by mass, and an isoparaffin content of 70% to 85%by mass.

In addition, it can also be prepared by being blended with a solvent ora blendstock obtained from each unit of a petroleum refinery plant asappropriate to meet the composition of the gas oil composition of thepresent invention.

EXAMPLES

The present invention will now be described in more detail withExamples; however, the invention is not limited to any of the followingExamples.

It should be noted that analysis methods for each property in Examplesare as follows.

-   Sulfur content: Measured according to JIS K 2541 “Crude oil and    petroleum products—Determination of sulfur content”-   Aromatic content: Measured according to JIS K 2536-3 “Determination    of aromatic components by gas chromatography”-   Distillation property: Measured according to JIS K 2254 “Petroleum    products—Determination of distillation characteristics”-   Density: Measured according to JIS K 2249 “Crude petroleum and    petroleum products—Determination of density and petroleum    measurement tables based on a reference temperature”-   Kinetic viscosity: Measured according to JIS K 2283 “Crude petroleum    and petroleum products—Determination of kinematic viscosity and    calculation of viscosity index from kinematic viscosity”-   Flash point: Measured according to JIS K 2265 “Crude oil and    petroleum products—Determination of flash point”-   Cetane index: Measured according to JIS K 2280 “8. Calculation of    cetane index by the four-variable equation”-   Cloud point: Measured according to JIS K 2269 “Testing methods for    pour point and cloud point of crude oil and petroleum products”-   Cold filter Plugging point: Measured according to JIS K 2288    “Petroleum products—Diesel fuel—Determination of cold filter    plugging point”-   Pour point: Measured according to JIS K 2269 “Testing methods for    pour point and cloud point of crude oil and petroleum products”

Paraffin content, isoparaffin content: the paraffin content andisoparaffin content per carbon atom were measured using GC-FID. Thecalculation was performed using values measured using a temperatureprogram (column oven temperature: heated at 8° C./min from 140° C. to355° C., sample injection temperature: 360° C., detector temperature:360° C.) at a carrier gas (helium) flow rate of 1.0 mL/min using anonpolar column (stainless steel capillary column ULTRA ALLOY-1) and anFID (flame ionization detector).

(Light Gas Oil Blendstock, Heavy Gas Oil Blendstock)

A light gas oil blendstock and a heavy gas oil blendstock were preparedin accordance with the following procedure.

An FT synthetic oil obtained by FT synthesis was used and a lightfraction of the FT synthetic oil was subjected to hydroisomerization(LHSV: 1.8 h⁻¹, hydrogen partial pressure: 3.0 MPa, reactiontemperature: 320° C.). After that, the resultant hydroisomerized oil anda hydrocracked oil obtained by performing hydrocracking (LHSV: 1.8 h⁻¹,hydrogen partial pressure: 4.0 MPa, reaction temperature: 310° C.) on awax fraction of the FT synthetic oil were mixed while recycling(recycling rate: 50 vol %) a bottom oil (fraction at the cuttingtemperature: not less than 360° C.) of a product fractionator, and themixture was then supplied to the product fractionator. Subsequently, themixture was fractionated by the product fractionator, thereby obtainingthe light gas oil blendstock and the heavy gas oil blendstock. Thecutting temperature of the light gas oil blendstock and the heavy gasoil blendstock was 250° C.

The composition of the obtained light gas oil blendstock 1 and the heavygas oil blendstock 1 is shown in Table 1.

Examples 1 to 4, Comparative Examples 1 and 2

Light gas oil blendstocks and heavy gas oil blendstocks were mixed basedon the mixing ratios shown in Table 1. A cold flow improver (InfineumR240 manufactured by Infineum Japan Ltd.) was added at 200 ppm by massto the mixture, thereby obtaining gas oil compositions used as samples.

For the gas oil compositions obtained in Examples and ComparativeExamples above, after the properties were measured (note that thedistillation temperature, cloud point, flash point, and cetane indexwere measured only with respect to Example 2, Comparative Example 1, andComparative Example 2), the pour point and kinetic viscosity wereevaluated. The results are shown in Table 1.

As for the conditions suitable for use under very low temperatureweather conditions, cases where the requirements for the pour point of−70° C. to −35° C. and the kinetic viscosity at 30° C. of 1.5 mm²/s to4.0 mm²/s were met were evaluated as “preferable (+)”, whereas caseswhere the requirements for the pour point of −66° C. to −55° C. and thekinetic viscosity at 30° C. of 2.0 mm²/s to 3.5 mm²/s were met wereevaluated as “particularly preferable (++)”. On the other hand, caseswhere none of the above conditions were met were evaluated as “poor(−)”.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 1 Example 2 Light gas oil blendstock vol % 20 40 60 80 0 100Heavy gas oil blendstock vol % 80 60 40 20 100 0 CFI Addition amountmass ppm 200 200 200 200 200 200 5% Distillation temperature ° C. 187.5252 165 50% Distillation temperature ° C. 251 293.5 197 95% Distillationtemperature ° C. 322 339 238 97% Distillation temperature ° C. 329 346242 Sulfur content ppm <1 <1 <1 <1 <1 <1 Aromatic content mass % <1 <1<1 <1 <1 <1 Density g/cm³ 0.776 0.769 0.762 0.755 0.783 0.749 Cloudpoint ° C. −56 −6 ≦−25° C. Pour point ° C. −56 −58 −57 −53 −54 −53 Flashpoint ° C. 59 88 48 Cetane index 84 94.4 73.1 Paraffin content mass %≦99.5 ≦99.5 ≦99.5 ≦99.5 ≦99.5 ≦99.5 C5-15 Paraffin content mass % 40 5569 84 26 99.7 C20-27 Paraffin content mass % 14 11 7 4 17 0 Isoparaffincontent mass % 71 66 59 54 76 48 Normal paraffin content mass % 29 34 4146 24 52 Normal paraffin content/ mass % 0.4 0.5 0.7 0.9 0.3 1.1Isoparaffin content Pour point ° C. −56 −58 −57 −53 −54 −53 Kineticviscosity 30° C. mm²/s 3.2 2.5 2.1 1.7 4.1 1.4 Evaluation ++ ++ ++ + − −

The results in Table 1 show that the gas oil compositions obtained inExamples had good quality even if they were used under very lowtemperature weather conditions, and in particular, Examples 1 to 3 thatmet the preferred ranges of the present invention achieved betterquality.

On the other hand, for the gas oil compositions obtained in ComparativeExamples, it was found that they deposited in the form of wax under verylow temperature weather conditions or their kinetic viscosity wasinsufficient.

INDUSTRIAL APPLICABILITY

The present invention has particularly advantageous effects in that agas oil composition providing superior low temperature performance ascompared with the case of using the conventional techniques can beprovided and an oil having a high normal paraffin content, such as FTsynthetic oil can easily be used as a feedstock of the gas oilcomposition.

1. A gas oil composition, wherein a sulfur content is 1 ppm by mass orless, an aromatic content is 1% by mass or less, a C5-C15 paraffincontent is 30% to 85% by mass, a C20-C27 paraffin content is 3% to 20%by mass, and a isoparaffin content is 50 to 75% by mass, characterizedin that the gas oil composition comprise a cold flow improver at 20 ppmto 1000 ppm by mass.
 2. The gas oil composition according to claim 1,wherein a pour point is −70° C. to −35° C. and a kinetic viscosity at30° C. is 1.5 mm²/s to 4.0 mm²/s.
 3. The gas oil composition accordingto claim 1, comprising Fischer Tropsch synthetic oil.